Classifications

• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09B—EDUCATIONAL OR DEMONSTRATION APPLIANCES; APPLIANCES FOR TEACHING, OR COMMUNICATING WITH, THE BLIND, DEAF OR MUTE; MODELS; PLANETARIA; GLOBES; MAPS; DIAGRAMS
  • G09B23/00—Models for scientific, medical, or mathematical purposes, e.g. full-sized devices for demonstration purposes
  • G09B23/28—Models for scientific, medical, or mathematical purposes, e.g. full-sized devices for demonstration purposes for medicine
  • G09B23/288—Models for scientific, medical, or mathematical purposes, e.g. full-sized devices for demonstration purposes for medicine for artificial respiration or heart massage

Definitions

• This invention relates to a system and method for validating or verifying the performance of a QCPR device.
• the ILCOR/ AHA Guidelines [1] recommend how cardiopulmonary resuscitations (CPR) should be carried out.
• CPR cardiopulmonary resuscitations
• the Guidelines set targets for CPR parameters such as chest compression depth, chest compression rate, ventilation rate, ventilation inspiration time etc.
• these guidelines are not always followed in practice [2-3]. Therefore, it has been proposed to develop systems that give audible or visual feedback to the rescuer on how his or hers CPR performance adheres to the Guidelines.
• Feedback on compressions is often based on measurements of the compression depth waveform using a chest pad equipped with an accelerometer and optionally a force sensor. Based on the measured acceleration, chest depth can be obtained by double integration, for instance using the signal from the force sensor to reset depth to zero for each compression.
• the force signal can also be used to give feedback on leaning, i.e. incomplete release of the compression force between compressions.
• Ventilation feedback may for instance be based on measurements of intra-thorax impedance between defibrillation pads, a measurement that has been found to correlate well with ventilation activity [4].
• Other methods for measuring ventilations include measurements of pressure, flow, temperature, sound, humidity, chest circumference of chest rise.
• CPR feedback algorithms To convert these physical measurements of acceleration, force and impedance (or other relevant parameters) to CPR parameters related to compressions and ventilations, mathematical algorithms are needed. These will in the following be termed CPR feedback algorithms.
• CPR feedback algorithms To have CPR feedback systems approved for clinical use by regulatory authorities, the CPR feedback algorithms must be qualified (verified, validated) to assure that the required CPR parameters are measured with a sufficient accuracy.
• a qualification of the feedback system and its algorithms may for instance be carried out by testing the system out in the environment in which it is intended to be used, e.g. during ongoing resuscitation attempts. This may often be a lengthy and time- consuming exercise, and it may be difficult to get approval to conduct such experimental studies on human subjects undergoing CPR.
• CPR feedback algorithms depend on a number of parameters, including the physical characteristics of the human subjects undergoing CPR and also on the way CPR is performed. Using only field data from actual resuscitation attempts, it will therefore be extremely time consuming to assure that all realistic combinations of patient characteristics and CPR parameters (e.g. compression depth, compression rate, compression duty cycle, ventilation rate, inspiration time, volume given) are covered. A complete, realistic range of CPR parameters can however easily be covered in a controlled environment, for instance by performing CPR on manikins.
• CPR parameters e.g. compression depth, compression rate, compression duty cycle, ventilation rate, inspiration time, volume given
• a manikin is a dummy human body or thorax containing structures that mimic human physiological elements important for training of CPR skills, such as an inflatable lung and an airway for practicing ventilation through the mouth of the manikin, and a spring loaded chest to practice chest compressions.
• CPR skills such as an inflatable lung and an airway for practicing ventilation through the mouth of the manikin, and a spring loaded chest to practice chest compressions.
• the characteristics of most available manikins are not very representative of the human population, nor do they span the actual range of physical properties found in the population.
• the aim of this invention is to describe a method to qualify (verify, validate) feedback related algorithms for CPR, so that these algorithms can be tested across a broad range of both patient characteristics and CPR parameters.
• CPR with different parameters can either be delivered manually, e.g. by trained rescuers, or by means of a machine that is programmed to deliver CPR with the given parameters.
• the object of the invention is to facilitate qualification of CPR aiding and feedback equipment, by constructing manikins with a range of physical properties representative of properties found in the population, thus improving the efficiency of this verification by avoiding the use of testing on patients.
• the method can for instance consist of the following steps:
• Manipulate said physical property data for instance by statistical methods, to represent a range of values found in the population.
• - Construct manikins or other functional elements with properties that mimic said representative range of values for each physical property.
• different values of a given physical property can either be realized in a single manikin with means for selecting between different values, or in different manikins, each having one or several of the desired parameter values.
• manikins that mimic different physical properties, such as one manikin for ventilations and one for compressions.
• the manikins do not have to have the form of human bodies, but can be purely functional devices that mimic the desired property, such as for instance a combination of a spring and a damper designed to be compressed in a CPR-like manner.
• the word "manikin” is therefore used in a wide sense and covers any device or machine that is intended to mimic the properties of any part of the human body relevant to CPR.
• the span of values of a certain parameter to represent the population can be based on the collected population data using any type of statistical method. They may for instance be medians, percentiles, means or cumulative values of a distribution function, e.g. a normal or a lognormal distribution.
• Important CPR parameter measurements to qualify include: - Compression activity
• Figure 1 illustrates a schematic equivalent of the relevant physical characteristics of a chest being treated with CPR.
• Figure 2 illustrates a possible embodiment of a manikin simulating the parameters illustrated above.
• Figure 3 illustrates a more complex version of the embodiment illustrated in figure
• Figure 4 illustrates a flow chart of the method according to the invention.
• Figure 1 shows a schematic model of the human or a manikin chest comprising an elastic element 1 (e.g. a spring) with non-linear properties and a damping component 2 that is predominantly viscous.
• the human or manikin chest consists of a depth- dependent stiffness k(x) in parallel with a depth dependent damping parameter ⁇ (x).
• the stiffness and damping characteristics k(x) and ⁇ (x) of human chests may be derived from simultaneous measurements of force and depth on patients undergoing CPR, for instance using a mechanical compression device or a chest pad with an accelerometer and a force sensor. From acceleration, depth can be obtained by double integration.
• the viscous component of the force must first be subtracted from the total force, for instance by assuming a viscous damping parameter being dependent of depth and giving rise to a damping force proportional to the speed of the chest (F_v ⁇ v, where F_v is the viscous force, ⁇ is the damping parameter and v the speed of the chest).
• the value of the damping parameter ⁇ at different depths x can be estimated by observing the width of the hysteresis loop in the force-depth curve.
• the moving mass of the chest giving rise to inertial forces, can also be estimated by correlating acceleration and force, for instance near the minimum or maximum points of compression where the viscous force is low.
• the target reference characteristics of the manikins may be chosen to represent specific parts or ranges of the population with respect to stiffness, damping and/or mass.
• the chest stiffness is realized as an elastic element 1, and can for instance be realized in the form of mechanical springs, or as gas springs.
• the springs 1 may preferably have progressive characteristics to match the stiffness data found in the population.
• the population may be grouped in n groups in order of increasing stiffness.
• One spring type may then be defined for each group, so that the n springs range in stiffness from "softest chest” to "stiffest chest".
• the n springs may for instance be interchangeable in the manikin itself, or there may be one manikin for each group.
• the number of groups can for instance be between 1 and 20.
• Patients can also be grouped based on other parameters, for instance age, or grouped as infants/pediatric/adults.
• a viscous damper 2 may for instance be realized by causing the compression movement to squeeze a viscous medium (air, water, oil) out through a slit of appropriate width. This gives predominantly viscous damping mechanism, which supplies a force F v against the movement being proportional to the speed v of the chest during compression.
• the damping coefficient ⁇ F v /v can be made to vary with compression depth.
• Figure 2 shows a possible construction of a chest spring 1 and damper mechanism.
• the spring 1 is preferably a progressive spring.
• the damper mechanism is a piston 3 with a surrounding cylinder 7 or equivalent filled with air, in which there is a flow restriction 4 limiting the flow of air between the interior of the cylinder 7 and the ambient.
• the flow restriction 4 can for instance have form as a narrow gap between the piston outer diameter and the cylinder inside diameter.
• the volume of the air-filled interior of the cylinder 7 is determined by the position of the piston 3.
• the position of the piston 3 is preferably related to the position of the chest surface 5, so that when the latter is under compressions, the volume inside the cylinder changes. Due to the restriction 4 through which air has to pass to reach ambient pressure, this change in volume will create an under- or overpressure inside the cylinder 7, depending on whether the chest moves up or down.
• the flow resistance of the restriction 4 varies with compression depth. This can for instance be obtained by letting the length of the restriction 4 correspond to the position of the piston 3, as is the case with the embodiment shown in figure 2.
• the stiffness and damping elements are so constructed that when the spring 1 and damper 2 is mounted in the manikin or final system, the spring and damping of the entire manikin chest resembles a reference characteristics representative of the whole or a part of a population.
• the deviation from the reference characteristics can be assessed by measuring the force/depth characteristics for the manikin chest 6 under compression, and calculate the stiffness and damping, for instance using the same equipment and methods that were used for generating the basis data collected on the patient population.
• the depth reference measurement gives information that can be used to qualify all compression depth related parameters listed above.
• a separate force sensor can be used to validate the leaning force measurement.
• Thorax impedance sensitivity can be measured by ventilating human subjects with a controlled air volume and measuring the corresponding impedance change through defibrillation pads. Based on such measurements, the thorax impedance characteristics of the manikin(s) may be chosen to represent specific parts or ranges of the population.
• the population may be grouped in n groups in order of increasing sensitivity.
• One impedance sensitivity may then be defined for each group, so that the n springs range in sensitivity from "least sensitive” to "most sensitive”.
• the number of groups can for instance be between 1 and 20.
• a system with the defined thorax impedance sensitivities can then be realized, for instance based on the airway/lung system of a manikin. This can be accomplished by measuring changes in lung volume of the manikin caused by inspiration of air, for instance by the use of an encoder in the manikin. This signal can in turn be used to control the resistance of an electronic circuit that is connected to the defibrillation pads of the device with algorithms to be qualified. This can for instance be accomplished by means of a digitally controlled potentiometer.
• the mapping factor of encoder values to circuit resistance can be tailored to match the obtained impedance sensitivity being representative of the different groups of the population.
• An independent ventilation reference can be obtained by means of a flow sensing device, either mounted inside the airway of the manikin or between a ventilation bag and the mouth of the manikin. This measurement can be used to qualify all ventilation related parameters listed above.
• the monitoring tool to be tested and qualifies is not illustrated in the drawings, but may be any type of equipment described above for providing feedback or evaluations of CPR performed on a patient or manikin.
• the Heartstart MRx with Q-CPR device of Philips Medical and Laerdal Medical, cleared by the US Food and Drugs Administration (FDA) under K051134, is an example of a commercial device with this functionality.
• the monitoring tool includes sensors, e.g. for measuring force, movement, acceleration, ventilation or other parameters considered to be of interest for the CPR and corresponding to available reference parameters.
• the monitoring tool may also, as stated above, include algorithms for evaluating the measured parameters, e.g. for providing them with a format being comparable with the reference parameters. These sensors and algorithms are considered to be part of the known art and will not be described in detail here.
• the comparison of the parameters may simply include a simple analysis of the numerical deviation from the reference parameters or may be based on more complex statistical methods, e.g. analyzing deviation, multivariate methods etc.
• Figure 3 shows a more complex version of the embodiment illustrated in figure 2 with external volumes 11 - 12.
• the variable spring element 1 is obtained by compression of air, for instance by a piston 8 in a cylinder 9. Inside the cylinder 9, or in other volumes 11-12 coupled to the cylinder 9, there is a closed volume filled with air.
• the piston 8 is preferably fixed to the moving part of the manikin chest 6, so that when the manikin chest surface 5 moves up and down under compressions, the air volume in the cylinder 9 (and connected volumes 11-12) is compressed. The pressurized air will then act on the piston 8 with a force F given by the area A of the piston 8 and the overpressure/* inside the cylinder 9.
• connection tubes 14 to the external volumes may be so small that they act as flow restrictions.
• the air volume inside the cylinder 9 (and connected volumes 11-12) will change, and so also the zero force piston 8 position.
• the opening 15 must be so small that the typical time constant for air passing through the opening 15 is larger than typical compression time constants, yet so large than the time constant is smaller than the relevant thermal time constants of the system.
• Figure 4 illustrates the preferred method according to this invention based on the sampled reference data.
• a manikin e.g. of the type described above and in the abovementioned simultaneously filed Norwegian patent application 2006 2108, is provided with the chosen characteristics representing at least part of the population, and CPR is performed on the manikin.
• chosen CPR parameters for instance compression force or depth
• characteristic properties of these CPR parameters for instance maximum amplitude or frequency
• reference parameters for instance measured by an independent system. From this comparison the quality of the monitoring tools, both with respect to measuring and evaluation in producing relevant CPR parameters are evaluated. If the deviation between the two is too large the monitoring tool lacks the sufficient quality and the measuring system or algorithms may be adjusted.
• the invention thus relates to a system and method for controlling the output from a CPR monitoring tool, e.g. for providing feedback during CPR treatment, comprising the steps of providing a manikin having chosen characteristics represented by at least a part of the population, performing a CPR treatment on said manikin according to a predetermined procedure.
• These manikin properties may e.g. be based on statistically calculated data based on samples from CPR performed on patients, either by using available results from general studies and articles on the subject, or by studies aimed especially at this purpose.
• the CPR on the manikins may be performed by a person or simulator programmed to perform a certain CPR procedure.
• the monitoring tool measures and possibly also calculates chosen parameters related to the CPR treatment of the manikin and records the characteristic properties of said CPR parameters. If the CPR is performed by a simulator or other mechanism the reference parameters may be implicit and related directly to the procedure, so no parallel measurements are needed.
• the quality of the monitoring tool is assessed by comparing the measurement of said parameters provided by the monitoring means with corresponding parameters from a reference system, e.g. an independent, calibrated system, measuring the same parameters during CPR.
• the measured and evaluated parameters will be one or more of the parameters force, movement (like compression depth), leaning force, compression duty cycle, thorax impedance and ventilation.
• the quality calculation may include the comparison of the measured magnitude of said CPR parameter and/or the measured frequency of said CPR parameter with a reference value.
• the parameters to be measured and evaluated can be related to the physical properties of the patient instead of the characteristics of the CPR performed.
• said parameters related to physical properties of the patient as measured by the monitoring system will be compared to corresponding parameters as measured by a reference system. For instance, the chest stiffness of a patient will first be assessed by an independent system, and then measured by the monitor to be qualified. The difference between these two measurements may then be a measure of the quality of the monitoring tool.

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• 2006
  • 2006-05-10 NO NO20062107A patent/NO324802B1/no unknown
• 2007
  • 2007-05-07 WO PCT/NO2007/000160 patent/WO2007129908A1/en active Application Filing

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